Insulating oil



No Drawing.

Patented May 3, 1932 UITED JAMES G. FO RD, 0F WILKINSBURG, EENNSYLVANIA, ASSIG'NOR T6 WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A COR?ORATION OF PENNSYLVANIA.

went-Arrive can My invention relates to compositions of matter, and more particularly to an improved insulating oil for electrical apparatus and to i a method of producing same.

An object of my'invention is to provide a high-grade insulating oil for transformers or other oil-filled electrical apparatus that remains substantially permanent in its characteristics for a long period of time and which 10 is comparatively free from the tendency to develop sludge or acidity in service.

Another object of my invention is to provide a high-grade insulating oil that is substantially free from unsaturated aliphatic hydrocarbons and such aromatic hydrocarbons as develop asphaltic sludge in service but which contains a suflicient amount of resinous compounds which donot develop sludge to prevent the development of acidity in the oil. 7 Another object of my invention is to provide a method of preparing a high-grade irisulating oil for transformers or other oilfilled electrical apparatus that does not develop asphaltic sludge or acidity in service, which consists essentially in treating that fraction of crude oil referred to in the art as insulating oil with a suflicient quantity of 95 to 98% concentrated sulphuric acid and agitating the mixture for a sufficient length of time to remove all of the unsaturated aliphatic compounds and those aromatic compounds that have the tendency to develop sludge in service but leaving in the oil, or adding to it, a sufiicient quantity of residual resinous compounds which are not readily removed by a sulphuric acid of the concentration specified, and which are valuable constituents of high-grade insulating oils, as they prevent the formation of organic acids and intermediate oxidation products.

t is well known that'the constituents of crude oils vary considerably in accordance Application filed April 12,1928, Serial No. 269,616.

dizing influence of the air at elevated temperatures.

llt is an essential feature of my invention to prepare an oil from crude petroleum, irrespective of the source from which the crude oil is obtained, that is comparatively free from unsaturated aliphatic hydrocarbons and aromatic hydrocarbons that form sludge in service but contain a suflicient quantity of residual petroleum resins of a type which prevents acidity from developing in the oil when it is exposed to the oxidizing influence of the air at the operating temperature of the apparatus. The amount of these compounds. is so small that they will not form appreciable quantities of sludge in service.

It has previously been the practice, in preparing insulating oils, to distill OK the volatile products from the crude oil and collect upon the composition of the crude oil from which the insulating fraction was obtained Such oil is not suitable as an insulating oil to be utilized in transformers because, when heated in service and exposed to the oxidizing action of the air, an asphaltic sludge is formed which settles upon the working parts of the transformer or other electrical apparatus and prevents the dissipation of heat, thereby causing excessive operating temperatures.

It is known that the tendency of insulating oils to form asphaltic sludge is caused by the presence of unsaturated aliphatic and certain aromatic hydrocarbons. It has, therefore, been proposed to agitate the oil with oleum or fuming sulphuric acid to reacid is neutralized by an alkali, such as a dilute solution of sodium carbonate, or sodium hydroxide, and to subsequently filter it through fullers earth or silica gel. Since fuming sulphuric acid, if utilized in sufficient quantities, is highly efficient in removing all unsaturated aliphatic and aromatic hydrocarbons, a water-white oil is produced by this method which is substantially free from these ingredients.

Such oil is not much more efficient as an insulating oil for transformers and other electrical apparatus than-the one previously described because, when it is exposed to the oxidizing influence of the air, at the operat ing temperature of the electrical apparatus, for a short period of time, an excessive quantity of organic acids, or intermediate oxidation products, such as alcohols, aldehydes, ketones, and possibly peroxides, are formed which attack and weaken the mechanical strength of the insulation. The organic acids also react with the scale and metallic parts of the transformer and transformer casing, such as copper, iron, lead or tin, forming metallic soaps that impart emulsifying characteristics to'the oil. The water solubility of an oil prepared in the manner specified also increases with acidity and when such oils become saturated at the operating temperature of the apparatus, the amount of water precipitated when the oil is subsequently cooled, substantially lowers the dielectric stren h of the oil.

I have discovere that an oil of the desired properties may be produced by removing all of the aliphatic unsaturated" hydrocarbons from the insulating oil and those aromatic hydrocarbons which develop sludge in service, leaving inthe oil or adding to it a sufficient amount bf an anti-oxidizing agent that is composed of resinous compounds that have characteristic aromatic reactions which do not develop sludge but which are effective in preventing acidity. My improved oil is very eflicient when utilized intransformers as, when exposed to the oxidizing influence of the 'air at elevated temperatures only very small amounts of sludge or acidity will develop in a comparatively long-period of time.

In practicing my invention, the insulating fraction of the crude oil is obtained in the usual manner; that is, by first removing the volatile constituents, such as petroleum ether, gasoline and kerosene, by distillation and then collecting that portion of the oil having a viscosity of to seconds at 100 F. when measured by the Saybolt viscosimeter. This oil, which is known in the art as an insulating oil", contains unsaturated aliphatic compounds, such as olefines, polyolefines, and terpenes, and naphthenes, as well as a considerable quantity of aromatic compounds. I then treat this fraction with about 25%, by volume, of sulphuric acid having a concentration of from 95% to 98% and agitate the mixture for approximately two hours.

It is an essential feature of my invention that the quantity of acid utilized and the time of agitation shall be sufiicient to remove allof the unsaturated aliphatic hydrocarbons and most of the aromatic hydrocarbons. I have found that it is necessary to add from'l5 to 50% acid and to agitate the mixture for from one-half hour to two hours or until there is no further absorption of the oil by the sulphuric acid. The amount of sulphuric acid employed may, of course, be varied, and the time of agitation will depend, to a considerable extent, on the amount of sulphuric acid utilized. It will be understood, however, that sufiicient sulphuric acid.

must be employed to insure the removal of all constituents'of the oil which may be removed by acid of the concentration specified. Large quantities of acids are not harmful but, for economic reasons, it is desirable to utilize as small a percentage of acid as possible which is consistent with a thorough removal of all unsaturated hydrocarbons and those aromatic hydrocarbons that may readily be removed by an acid of this concentration. If additional sulphuric acid of this concentration, when agitated with the oil for a short period, will effect an additional removal of unsaturated hydrocarbons, it is an indication that either the amount of sulphuric acid or the time of agitation was not sufficient.

After the oil is treated with the acid and agitated for a sufficient length of time, the acid sludge is allowed to settle to the bottom of the container or, if preferred, it may be centrifuged until the 011 becomes clear and no longer increases in volume. The oil is then decanted from the acid sludge, and the residual acid present in the oil is neutralized by an alkali, such as a dilute solution of sodium carbonate or sodium hydroxide, is washed with water and dried. The oil is then treated with a small amount of absorbent material, say about x 94), by weight, of silica gel or fullers earth, or a mixture thereof, to improve its color and its resistance to emulsification.

The insulating oil fraction obtained from a Gulf Coast crude oil, when treated by my improved process, did not form iodine addition products, indicating the absence of unsaturated aliphatic compounds. None of the oil was absorbed after being agitated for two hours with sulphuric acid having a concentration of 95 to 98%. Its nitration value,

" when treated by the method of Eglofl' and Morrell, (Journal Industrial and Engineering Chemistry, vol. 18, page 354) indicated that it contained as high as 5% aromatic neaavoo compounds which, when treated with concentrated sulphuric acid, were only very slowly sulphonated. Tests upon the oildem onstrated that it was very stable when exposed to the oxidizing actions of the air at temperatures ranging from 80 to 120 C. The quantity of acid formed over a long period of time was practically negligible and the amount of sludge formed was very small and showed very slight acceleration.

I have found, by numerous tests, that the oil owes its stability to the total absence of unsaturatedaliphatic compounds and to the small amount of residualresinous compounds that are aromatic in nature; that 1s, they have reactions that are characteristic of aro matic compounds. v These compounds are incapable of, being absorbed by sulphuric acid having a concentration of from 95 to 98% during the time of agitation.

It is possible to separate these anti-oxidizing compounds from the oil by treating the oil with an adsorption agent, such as silica gel, fullers earth or carbon black, and the anti-oxidizing compounds may, in turn, be

readily isolated from the adsorption agent by means of acetone. 7 Upon examination, it has beenfound that they are resinous in character and impart a slightly yellowish tint to the oil. They respond to reactions that are characteristic of aromatic compounds and are an essential constituent of my improved oil. I have designated these compounds residual resinous compounds, because they are highly viscous and tacky and it is impossible to remove them from the oil by agitatingthe oil from one-half to two hours -with a sulphuric acid having a concentration r 95% to 98%.

In order to prevent acidity, it is necessary that .these residual resinous compounds, which are either present in the original oil or are the polymerization products of ter penes, polyterpenes, or similar compounds. formed by the action of a sulphuric acid of the concentration specified,- shall be present in amounts ranging from .1 to 6%. Large quantities are not desirable" as increased amounts may cause the formation of sludge. A suflicient amount should be present, however, to prevent acidity from developing in the oil at the operating temperature of the apparatus. v

The residual resinous compounds are an essential constituent of the oil because, if they are removed by suitable means, such as treatment of the oil with fuming sulphuric acid, a water-white oil is produced which forms excess quantities of organic acids and intermediate oxidation products when utilized in service.

When the amount of resinous compounds by compounding it in the desired proportions with an oil of the water-white variety or, if desired, when the amount of the residual resinous compounds is relatively small and the oil has a tendency to develop acidity in service, an oil having the proper constituency may be prepared by compounding the oil having a relativelysmall amount of residual resinous compounds with one having a relatively large amount" of these compounds. Tn this manner, I am enabled to .obtain an insulating oil for transformers or other oil-filled electrical apparatus which contains the desired ingredients and which is. accordingly, highly efficient in service.

Water-white oils, or oils prepared in themanner specified, that contain only a relatively small percentage of residual resinous compounds, may also be rendered stable by adding a small percentage of the polymerization products of turpentine to them. Such polymerization products of turpentine may be prepared by adding sulphuric acid to turpentine and agitating the mixture while maintaining the temperature constant. The mixture is allowed to stand until the sulphuric acidihas settled to the bottom of the container, after which the sulphuric acid is separated from the polymerized turpentine product. The polymerized turpentine is then neutralized with alkali, such as a dilute solution of sodium carbonate or sodium hydroxide. About .1 to 5% of the turpentine polymerization product is generally considered effective for my purpose.

While I have described a specifiedform of my invention, it will be understood that various modifications may be made therein without departing from the spirit of my invention. T desire, therefore, that only such limitations shall be imposed upon my invention as are required by the prior art and the appended claims.

T claim as my invention:

1. The method of preparing an oil fqr transformers or other oil-filled electrical apparatus which comprises treating an insulating oil with from 15% to by volume, of 95% to 98% concentrated sulphuric acid and agitating the mixture for a sufficient length of time to remove substantially all unsaturated aliphatic compounds and all aromatic compounds that may be readily removed by acid of such concentration.

2. The method of preparing an oil for transformers or other oil-filled electrical apparatus which comprises treating an insulating oil with from 15% to 50%, by volume, of 95% to 98% concentrated sulphuric acid and agitating the mixture for from one-half hour to two hours.

3. The method of preparing an oil for transformers or other oil-filled electrical apparatus which comprises treating an insulating oil with from 15% to 50%, by volume, of

95% to 98% concentrated sulphuric 'acid and agitating the mixture for from one-half hour to two hours to remove substantially all unsaturated hydrocarbons and those aromatic hydrocarbons that have the tendency to develop sludge in service and then treating the oil with a small amount of an absorbent material to improve its color and increase its resistance to emulsification. 4. An insulating oil for transformers or other oil-filled electrical apparatus comprising saturated hydrocarbons and a suflicient quantity of polymerized hydrocarbons of the terpene group to prevent development of acidity, said oil being substantially free from unsaturated aliphatic hydrocarbon compounds and aromatic compounds which have the tendency to develop sludge in service.

- 5. An insulating oil for transformers or other oil-filled electrical apparatus comprising saturated aliphatic hydrocarbons, naphthenes, and a suflicient quantity of polymerized hydrocarbons of the terpene group .to prevent development of acidity, said oil being substantially free from unsaturated aliphatic hydrocarbon compounds and aromatic compounds which have thetendency to develop sludge in service.

In testimony whereof, I have hereunto sub scribed my name this 10th day of April, 1928. I JAMES G. FURD. 

